Photoconductive powders and a method for producing the same

ABSTRACT

A manufacturing process for producing an electrophotographic photoconductive power material comprising the steps of dispersing synthetic resin monomer and powdered photoconductor particles in a liquid dispersion medium which is not compatible with the said monomer, and while maintaining such dispersed condition, polymerizing the monomer to form polymer particles containing the photoconductor particles therein.

United States Patent Inventors HiroyuklKaneko;

Keitaro Ohe; Shigero Sadamatsu; Daiiiro Nishio, all of Kanagawa, Japan App]. No. 704,270 Filed Feb. 9, 1968 Patented Dec. 7, 1971 Assignee Fuji Photo Film Co., Ltd.

Kanagawa, Japan Priority Feb. 9, 1967 Japan 42 355; Feb. 9, 1967,42/8554 References Cited UNITED STATES PATENTS 3/1942 Depew 106/296 Primary Examiner-George F. Lesmes Assistant Examiner-John C. Cooper, 111 AnameySughrue, Rothwell, Mion, Zinn & Macpeak ABSTRACT: A manufacturing process for producing an electrophotographic photoconductive power material comprising the steps of dispersing synthetic resin monomer and powdered photoconductor particles in a liquid dispersion medium which is not compatible with the said monomer, and while maintaining such dispersed condition, polymerizing the monomer to form polymer particles containing the photoconductor particles therein.

PHOTOCONDUCTIVE POWDERS AND A METHOD FOR PRODUCING THE SAME BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to photographic powders for electrophotography utilizing a layer of photoconductive powder as a photosensitive layer and also to a method of producing the photoconductive powders.

2. Description of the Prior Art There is known an electrophotographic process of forming an image on a conductive or photoconductive substrate by applying thereto photoconductive powders. By the known process, a layer of charged photoconductive powders having a uniform thickness is formed on a conductive or photoconductive substrate or base and the powder layer is image exposed to provide an electrostatic latent image thereon according to density (the extent of brightness or darkness) of the image exposure. In this case, the electrostatic latent image of the portions having high image density, that is, the dark portions or those exposed to light of weaker intensity, has a relatively high potential and hence the electrostatic attractive force between the powder layer and the substrate is strong, while the latent image of the portions exposed to light of high intensity has low potential and hence the electrostatic attractive force between the layer and the substrate is relatively weak. Thus, by removing the photoconductive powders on the substrate by applying an external physical force in proportion to the extent of the attractive forces, a powder image is obtained on the substrate. The powder image may be fixed using heat, a solvent, or a solution of binder.

Conventional photoconductive powders to be employed in such electrophotography may be produced by pulverizing a mixture comprising powders of a photoconductive material dispersed in an appropriate insulating resin, but they are generally low in sensitivity and high in background density, for which reason it is difficult in many cases to obtain a highquality sharp image. This is deemed to originate in the fact that a substantial increase of conductivity corresponding to the quantity of radiating light cannot be obtained in the lower part of the powder layer and the depowdering characteristics are poor due to inappropriate geometrical size and configuration of the photoconductive powders and so on. Accordingly, these problems may be solved if it were possible to control the surface condition, grain size and configuration of the photoconductive powder as desired. As a result of investigation on the problems, the present inventors have come to achieve the present invention by finding a process for manufacturing photoconductive powder under which the said factors may be controlled as desired. The photoconductive powder manufactured by the process exhibits excellent electrophotographic characteristics.

SUMMARY OF THE INVENTION That is, an object of the present invention is to provide a process of manufacturing photoconductive powders possessing excellent electrophotographic characteristics. A feature of the process is that at first a synthetic resin monomer and powdered photoconductor are respectively dispersed in a liquid dispersion medium having little compatibility with the said monomer, or a synthetic resin monomer comprising a powdered photoconductor dispersed therein is dispersed in a liquid dispersion medium having little compatibility with the said monomer, and while maintaining such dispersed condition, the monomer is polymerized.

Another object of the present invention is to provide a photoconductive powder composition comprising a powdered photoconductor and a synthetic resin. A feature of the composition is that said powdered photoconductor particles are densely dispersed in the portion near the surface of said synthetic resin particle. The composition may be synthesized according to above process of polymerization.

DETAILED DESCRIPTION OF THE INVENTION Any suitable synthetic resin monomer may be available as the monomer for this electrophotographic photoconductive material, such as styrene and its derivatives; vinyl halides, such as vinyl chloride; ethylenically unsaturated monoolefines, such as ethylene; vinyl esters, such as vinyl acetate; esters of acrylic acid, such as ethyl acrylate; esters of methacrylic acid, such as methylmethacrylate; acrylonitrile; methacrylonitrile; acrylamide; methacrylamide vinyl ethers, such as vinyl isobutyl ether; vinyl ketones, such as vinyl hexyl ketone; vinylidene halides, such as vinylidene chloride; N-vinyl compounds, such as N-vinyl carbazole. Other nonvinyl-type thermoplastic synthetic resins are also available independently or as mixture of several monomers.

Any suitable powdered photoconductor may be available as the photoconductive material for this electrophotographic photoconductive material; selenium, sulphur cadmium sulphide mercuric iodido, zinc oxide, titanium oxide, anthracene, a photoconductive organic pigment or a nonphotoconductive powder coated with photoconductive material on its surface.

Mixture of several powdered photoconductor materials may also be used. A powdered photoconductor treated with dyes or other color forming materials under the influence of heat or reagents, sensitizers, resins, or other materials may also be used. A treating agent which considerably reduces the photoconductivity of the photoconductive material cannot be used.

Also, the photoconductive powder of the synthesized photoconductive powder which is treated with dyes or other color forming materials under the influence of heat or reagents may be available. For instance, methacrylic esters, acrylic esters, styrene and its derivatives vinyl chloride and vinyl acetate, etc., may be applied independently or in mixture of two or more of them. Also any suitable powdered photoconductor may be available,,for example, zinc oxide, titanium oxide, selenium, cadmium sulfide, cadmium selenide and conventionally known organic photoconductive materials, etc., may be applied.

According to the present invention, the photoconductive powder and the monomer respectively, or the monomer comprising the powdered photoconductor dispersed therein, are dispersed in a liquid medium which has little compatibility with the monomer and polymerized at an appropriate temperature while being maintained in the dispersed condition. For the purpose of dispersing the monomer and powdered photoconductor uniformly, an appropriate mixing or agitating device or ultrasonic dispersion device may be employed. In this case, appropriate additives, such as dispersion stabilizers, emulsifiers, etc., may be applied to this system. If required, a polymerization initiation may be added at any time before polymerization in relation to the monomer. After termination of the polymerization reaction, the synthesized photoconductive powder particles may be obtained by separating the particles out of the system by means of a filtering or centrifugal device, etc., and drying them.

Though fundamental characteristics of the photoconductive powder obtained in this manufacturing method depend on the combination and quantity ratio of powdered photoconductor and monomer to be employed, it may be possible to control the particle size and its distribution of the synthesized particles in spherical form by properly selecting the quantity ratio of the above-mentioned components to the liquid medium agitating strength, use of initiator, dispersion stabilizer or emulsifier, and their type and quantity, polymerization temperature, time and atmosphere. 1

Though the composition of the photoconductive powder obtained according to this method depends upon the type of the powdered photoconductor particles to be employed and the type of the monomer to be adopted, it is possible to control the distribution of powdered photoconductor particles in the synthesized photoconductive powder after termination of the polymerization if their combination was properly selected. For instance, it is possible to make the density of powdered photoconductor particles in the synthesized photoconductive powder rarer in the vicinity of the center and denser near the surface. It is also possible to cause almost all the powdered photoconductor particles to be localized near the surface. The photoconductive powder possessing such structure is superior in its electrophotographic characteristics to the one in which the powdered photoconductor particles are distributed uniformly on the whole.

The reason for this is believed to be based on the following considerations. That is, in cases where a uniformly charged layer of the photoconductive powder is formed, depending on the charging method, whether charging is effected simultaneously with dusting of the powder or after formation of the powder layer, the patterns of charge distribution on the surface of photoconductive powder particles may not be the same, but it is believed that nearly the entire surface bears electrostatic charges. in the case where a photoimage is radiated onto such a photoconductive powder layer, the rays of light reaching the lower part of the powder layer are the ones which having passed through the powder particles, except for those which pass through gaps among the particles of the powder layer, and their phototransmission is determined by scattering and absorption in the surface and interior of the powder particles. When charge transfer of interparticles of the photoconductive powder endowed with conductivity due to radiation of light is taken into account, in the photoconductive powder particles in which the powdered photoconductor particles are uniformly distributed on the whole, the increase of photoconductivity seems to be sufficient in the lower part of the powder layer due to scattering or absorption in the upper part of the layer. In comparison therewith, a photoconductive powder in which almost all the powdered photoconductor particles are located near the surface is extremely good with respect to phototransmission, and the charge transfer of interparticles of the powder takes place easily, even in the lower part of the powder layer, thus providing prominent electrophotographic characteristics.

As above, the photoconductive powder particles thus manufactured have a spherical shape, desired particle size and quite excellent electrophotographic characteristics.

The present invention is explained further in detail in the following examples, in which parts" refers to "parts by weight" if not otherwise indicated.

EXAMPLE I Photoconductive Cadmium Sulfide Powders l parts Styrene Monomer I00 pans Copper Stearate 0.1 part Benzoyl Peroxide 3 parts The components as shown were agitated to prepare a photoconductor dispersion liquid of monomer and the dispersion liquid was placed together with a proper quantity of distilled water into a separable flask, which was stirred to disperse the dispersion liquid in fine droplets. Then, maintaining the temperature of the system at 80 C. and stirring for 6 hours, the monomer was polymerized in pearl particles. The synthesized product was filtered and dried. As a result, a photoconductive powder the average particle size of which was 60 microns, was obtained. They were sieve sprinkled over a conductive plate in a quantity of 70 g./m. the photoconductive powder layer was charged in a dark place by means of a corona discharge device, and, after radiating a photoimage, the layer was suction developed by means of an air current. Thus, a quite satisfactory powder image could be obtained.

EXAMPLE 2 Pholoconductive Zinc Oxide I00 parts Ethyl Methacrylate Monomer 150 parts Copper Stearate 0.] part Benzoyl Peroxide 4.5 parts The components as shown above were mixed and the dispersion liquid thereof was placed in a separable flask. After the addition of 3,000 parts of distilled water, the composition was stirred and the temperature of the system was increased up to 70 C. to polymerize the monomer, and the polymerizing process was completed after 4 hours. The polymerized product was separated centrifugally and dried. Particles ranging from several to some 20 microns in particle size were obtained. The synthesized photoconductive powder was electrostatically dusted on a conductive plate at the dusting-on rate of 20 g./m., and, after radiation of a photoimage, the image was developed by blowing an air current thereon and a quite sharp powder image was obtained.

EXAMPLE 3 Photoeonductive Zinc Oxide 12 parts Methyl Methacrylate Monomer I parts Styrene Monomer parts Benzoyl Peroxide 3.5 parts The components as shown above were mixed and the dispersion liquid thereof was placed together with an aqueous solution of sodium polymethacrylate in a separable flask. While stirring the mixture and raising the system temperature up to 65 C., the above-mentioned monomers were copolymerized, and then filtered and dried. As a result, particles of about microns in the average particle size were obtained. Thereupon, tests were conducted to evaluate the electrophotographic characteristics thereof and satisfactory results were obtained. As a result of an examination of the cross section of these photoconductive powders by microscope, it was found that the zinc oxide, i.e., the photoconductive powder, existed densely near the surfaces, but was scarcely found near the centers of the particles.

EXAMPLE 4 A Phcteconductive Zinc Oxide 20 parts Distilled Water 400 parts 8 Methyl Methacrylate Monomer I00 parts Benzoyl Peroxide 3 parts After preparing independently the dispersion system components A and B, as shown above, both were placed in a separable flask, agitated and dispersed in fine droplets. Next, while feeding nitrogen gas and raising the system temperature up to 65 C., the above-mentioned monomer was polymerized, completing the polymerization after 3 hours. The photoconductive powder thus obtained was spray dried, whereby uniform particles, about 50 microns in the average particle size, were obtained. They were electrostatically dusted on a conductive plate at the dusting rate of 60 g./m. and, after radiation of a photoimage, the image was suction developed by means of an air current, whereby a quite excellent image was obtained.

EXAMPLE 5 Photoconductive Cadmium Sulfide 8 parts A Distilled Water 400 parts Sodium Polymethacrylate 0.4 part Methyl Methacrylate Monomer 50 part: B Styrene Monomer 50 parts Benzoyl Peroxide 3 parts After preparing independently the dispersion system components A, and B, as shown above, both were placed in a separable flask and while stirring the same and raising the system temperature up to 80 C., the above-mentioned monomers were copolymerized and upon completion, filtered and dried, whereby particles, about 120 microns in the average particle size, were obtained. Upon measuring the electrophotographic characteristic thereof, satisfactory results were obtained. As a result of examination of the photoconductive powders by various methods, it was confirmed that cadmium sulfide, the photoconductive powder, existed densely near the surfaces of the particles, but was scarcely found near the centers.

EXAMPLE 6 Photoconductive Zinc Oxide 50 part! A Photoconductive Cadmium Sulfide parts Distilled Water 400 parts B Ethyl Methacrylate Monomer I00 parts Benzoyl Peroxide 3 parts After preparing independently the dispersion system components A and B, as shown above, both were placed in a separable flask and stirred strongly, thus dispersing the monomer in fine droplets. The system was heated to cause polymerization, after which it was filtered and polymer particles were recovered and dried. As a result, photoconductive powder, ranging from several to some 30 microns in particle size, was obtained. The particles were dusted through a sieve onto a conductive plate, charged in a dark place by means of a corona discharge device, and, after radiation of photoimage, were blow developed by means of an air current, whereby a high-quality powder image was obtained.

EXAMPLE 7 photoconductive phthalocyanine pigment 4 parts A Sodium polymethacrylate 0.6 parts Distilled Water 400 parts Styrene Monomer 85 parts 8 Butyl methacrylate monomer l5 parts Benzoyl peroxide 3 parts After preparing independently the dispersion system components A and B, as shown above, both were placed in a separable flask and stirred strongly, thus dispersing the monomers in a fine granular form. Then the system was heated to cause polymerization, after which the reaction system was filtered and polymer particles were recovered and dried. As a result, photoconductive powder, about 90 microns in grain size, was obtained. The particles were dusted through a sieve onto a conductive plate, charged in a dark place by means of a corona discharge device, and, after radiation of a photoimage, the image was blow developed by means of an air current, whereby quite a sharp image was obtained.

EXAMPLE 8 Photoconductive Pl'ithalocyanine Pigment l5 parts Methyl Methuerylute Monomer I00 putt! Styrene Monomer 50 part! Benzoyl Peroxide 4.5 part:

The components as shown above were mixed and the dispersion liquid thereof was placed together with an aqueous solution or sodium polymethacrylate in a separable flask. While stirring the same and raising the system temperature up to 65 C., the above-mentioned monomers were copolymerized and the reaction system was filtered and the filter product was dried. As a result, particles, micron in the average grain size, were obtained. Thereupon, tests were made to evaluate the electrophotographic characteristics thereof and satisfactory results were obtained.

What is claimed is:

l. A manufacturing process for producing an electrophotographic photoconductive powder material comprising the steps of l) dispersing powdered photoconductive particles in an ethylenically unsaturated polymerizable monomer, (2) dispersing said dispersion as fine droplets in a liquid medium which is substantially nonmiscible with said monomer, and (3) maintaining said dispersion under polymerizing conditions thereby forming polymeric particles including the photoconductive particles.

2. A manufacturing process for producing an electrophotographic photoconductive powder material as claimed in claim 1, wherein said synthetic resin monomer is one selected from the group consisting of styrene and its derivatives; an ethylenically unsaturated monoolefin, a vinyl ester, an ester of acrylic acid, an ester of methacrylic acid, acrylonitrile, methacrylonitrile, acrylamide, methacrylamide, a vinyl ether, a vinyl ketone, a vinylidene halide, an N-vinyl compound, and

mixtures thereof.

3. A manufacturing process for producing an electrophotographic photoconductive powder material as claimed in claim 1, wherein said powdered photoconductive particles are selected from the group consisting of selenium, sulfur cadmium sulfide mercuric iodide, zinc oxide, titanium oxide, anthracene, a photoconductive organic pigment, a nonphotoconductive powder coated with a photoconductive material, powders of the foregoing photoconductors treated with color forming materials, and mixtures thereof.

l I i l 0 

2. A manufacturing process for producing an electrophotographic photoconductive powder material as claimed in claim 1, wherein said synthetic resin monomer is one selected from the group consisting of styrene and its derivatives; an ethylenically unsaturated monoolefin, a vinyl ester, an ester of acrylic acid, an ester of methacrylic acid, acrylonitrile, methacrylonitrile, acrylamide, methacrylamide, a vinyl ether, a vinyl ketone, a vinylidene halide, an N-vinyl compound, and mixtures thereof.
 3. A manufacturing process for producing an electrophotographic photoconductive powder material as claimed in claim 1, wherein said powdered photoconductor particles are selected from the group consisting of selenium, sulphur, cadmium sulphide, mercuric iodide, zinc oxide, titanium oxide, anthracene, a photoconductive organic pigment, a nonphotoconductive powder coated with a photoconductive material, powders of the foregoing photoconductors treated with color forming materials, and mixtures thereof. 